The objective of the proposed study is to further our understanding of the biochemistry of metachromatic leukodystrophy (MLD). MLD is a group of neurological disorders associated with dysfunctions in the catabolism of cerebroside sulfate (sulfatide). Classic MLD is characterized by progressive demyelination and neuropathy. At least seven different forms of MLD are now recognized and we know that it is not a simple, one gene-one enzyme-one mutation disease. A variety of mutations affecting more than one allelic site can cause dysfunctions of sulfatide catabolism and give rise to clinical MLD. The cerebroside sulfatase hydrolytic system must be viewed as a multi-component system. The amount and type of information needed to understand the biochemistry of MLD has expanded accordingly. Much of this information can be obtained by studying cerebroside sulfate hydrolysis in cultured cells. The present proposal consists of three components. The first phase will emphasize the cell biology of the intact fibroblast sulfatide loading test and characterization of the intracellular sulfatidase reaction. Each component of the system will be characterized with respect to parameters such as cell uptake, subcellular localization, optimal concentrations and in situ interaction with other components. These will serve as a base line for the second phase of the project which will focus on specific dysfunctions of cerebroside sulfate catabolism. Detailed studies will attempt to define the nature of specific lesions at the molecular level. The third component focuses on individual components of the CS metabolic system. Selected properties of highly purified enzyme and CS activator will be studied. Immunochemical techniques will be developed for monitoring synthesis, regulation, and turnover of the enzyme and activator proteins. DNA and RNA progenitors will be isolated, characterized, and their dynamic relationships explored. This information should facilitate accurate diagnosis, help define pathogenesis and contribute to the development of effective therapies.